Such test stands are used, in particular, for testing vehicles and vehicle components, such as, e.g., internal combustion engines, drive trains and brakes. The test specimen is thereby coupled to a load device and the load, which acts between test specimen and load device, is monitored. To test an internal combustion engine, the load device acts as brake and can be realized, e.g., by a dynamometer, a hydraulic brake, or an eddy current brake. To test a brake, the load device must be embodied as a drive device and can be realized, e.g., by a dynamometer (e.g., a direct current motor). The load device, the test specimen, and the measuring device are coupled to one another by suitable components, such as, e.g., drive shafts, couplers and levers, so as to be able to reliably transmit the acting torques and forces.
Different solutions are known as measuring devices. It is thus possible, e.g., to install a torque-measuring flange into the connecting strand between load device and test specimen. It is likewise known, e.g., to support the load device or also the test specimen so as to oscillate and to support the torques resulting during operation via a lever, which acts against a force-measuring device.
The testing of the test specimen typically requires an operation with different rotational speeds and torques, so as to be able to simulate an actual operation between idle state and full load.
The different components of a test stand respectively represent—mechanically abstracted—spring-mass systems. In particular, in the case of larger test stands, the components thus encompass relatively low natural frequencies. This also relates, in particular, to torsional vibrations.
The test specimens, as well as the load device, generate rotational vibrations and linear vibrations, which are introduced into the test stand and which are transmitted via the components of the test stand. Due to the fact that the test specimens can be operated in a wide speed range, it cannot be avoided that the vibrations generated by the test specimens coincide with resonance frequencies of other components of the test stand. The excitation of a component with a frequency in the natural frequency or resonance range, respectively, leads to an excessively strong vibration loading of the respective component and of the adjacent aggregates, whereby parts of the test stand can be damaged, but, at least, measuring results can be distorted.
In the event that vibrations, which coincide with resonance vibrations from one of the components, in particular, the measuring device, are generated during the operation of the test stand, strong vibration exaggerations occur at the respective component, which distort the measuring result or even make it impossible to measure the actual load.
It is known from German Published, Non-Prosecuted Patent Application DE 39 10 454 A1, corresponding to U.S. Pat. No. 4,989,458 to Suzuki, to correct the measuring signal with the help of an electronic circuit, so as to eliminate vibration influences in the vicinity of resonance frequencies.
Japanese Patent Document JP 58176531 describes a solution, in which a spring assembly is installed in the flux of force between a lever arm, which is fastened to a dynamometer that is supported so as to oscillate, and a force-measuring device that is connected to the end of the lever arm. Attempts are made with the help of the spring assembly to shift the natural frequency of the lever arm-force-measuring system into an uncritical range.
For the most part, measures for shifting the frequencies into overcritical or subcritical frequency ranges are not helpful in the case of test stands, because the test specimens are to be tested under conditions that are as real as possible. In this manner, a vibration-critical behavior, e.g., of a test specimen is to be determined. But, a shifting of resonance frequencies would prevent this.
The damping of the vibrations with the help of a coupling or compensating coupling, respectively, in the drive train or the reduction of the excitation (changing the test specimen itself) is also not acceptable in practice, because it calls into question the capability to transfer the test stand results to actual practice.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.